Hartiey—WMolecular Constitution of Supersacurated Solutions. 537 
instance, crystallizing to a solid mass by the introduction of an 
already formed crystal or a fragment of the same. ‘The facts of 
the case may be better understood by reference to a paper “On 
the Determination of the Solubilities and Specifie Gravities of cer- 
tain Salts of Sodium and Potassium,” by Page and Keightley.' 
The determination by saturation at a higher temperature 
and subsequent cooling proved that a state of supersaturation 
obtains less or more in every instance; but, in the case of these 
anhydrous salts, this phenomenon cannot be attributed to different 
. degrees of hydration, as in the case of sodium sulphate. The fact 
that solutions so prepared exhibit a greater density at 15°6° C. than 
those maintained at that temperature from the outset, has a 
probable explanation in what may be termed “the attraction of 
solution”; or in other words, “the indisposition of the salt to 
change its state by virtue of the attraction of the mass in solution.” 
The extent to which supersaturation can exist is shown by the 
subjoined figures, which were very exactly determined, and are 
quoted from the original communication. 
Solution prepared by digestion of thesalts {| Solution prepared by saturation at 100° C. 
at a constantly maintained temperature and subsequent cooling to 15°6° C. 
Ore WHGCOE 
Salt. Sp. Gravity. 100 parts of water Salt. Sp. Gravity. 100 parts of water 
dissolved. dissolved. 
NaCl 1204:08 35°76 NaCl 1206°93 36°26 
KCl LPO 32°88 KCl 1171-82 33°06 
NaNO, 1137°81 84°21 NaNO, 1378°43 84°69 
KNO, 1141°23 26°04 KNO, 1142-25 26°30 
KNO, \ 40°39 
and ( 
NaNO, ( 15°29 
together 
Nicol’s work is important, inasmuch as he furnishes evidence 
to disprove any analogy between the phenomenon of superfusion 
and that of supersaturation of a solution. Supersaturated solutions 
were prepared by dissolving cold dehydrated salts in cold water, 
and such solutions were found to be identical, so far as the 
quantity of dissolved salt is concerned, with solutions prepared by 
the aid of heat. He ascribed the formation of supersaturated 
solutions to the existence in solution of the anhydrous salt. 
According to this view, supersaturated solutions differ in no way 
1 Jour. Chem. Soc., vol. xxy., 1872, p. 566. 
